How do we know that Jesus' sacrifice was effective for salvation?

The effectiveness of Jesus' sacrifice is rooted in its divine nature and the fulfillment of God's plan. In John 17, Jesus speaks of having completed the work given to Him by the Father, which underscores the perfect obedience required for redemption. His sacrificial death was not only an expression of love but also a necessary act to satisfy God's justice. Unlike the temporary animal sacrifices of the Old Testament, Jesus' atonement was permanent and sufficient, ensuring salvation for those whom the Father has given Him, as stated in John 6:37.